Michigan Department of Natural Resources
Fisheries Research Report No.1859, 1978
Survival of Rainbow Trout Stocked in a Lake Superior Tributary, 1971-1973
Wilbert C. Wagner and Thomas M. Stauffer
Abstract.-Experimental plantings of marked domestic rainbow trout (30, 000) and steelhead (30, 000) were made in the Huron River near its mouth in May and June 1971-1973. Domestic trout were 19-month-old progeny of fall-spawning broodstock held in a hatchery and steelhead were 13-month-old progeny of spring-spawning wild trout from Lake Michigan. The purposes of the plants were to compare returns of adult domestic and steelhead to the angler, assess results of "'imprinting" and determine the effect of differences in water hardness between the hatchery and receiving water on early survival of planted trout. Return to the angler was assessed by examination of a portion (about 20%) of the anglers' catch in the Huron River at the times that trout in the plants were expected to mature and return to the Huron River. Trout were imprinted by holding them in cages in the river for about a week before release. Early survival was assessed by counts of dead trout on arrival at the river and by observation of mortality in samples of the plants that were retained in cages in the river.
Known results of adult trout to anglers were virtually nil (0. 005%) as were estimated returns (0. 06%). Other plantings of rainbow trout in Lake Superior tributaries have produced equally dismal results. The causes of the low return in our study were not identified, but stresses due to time in transit and transfer from hard (130-172 ppm, total hardness) to soft water (40 ppm) seemed to be contributing factors. For trout in transit for 9 to 13. 5 hours from the Platte River (160 ppm) and Oden (172 ppm)hatcheries, mortality for about 1 week after planting was 9-32%. in contrast, trout in transit for 5 hours from Thompson Hatchery (130 ppm) had no mortality for a comparable length of time. However, stress of transportation and water hardness change does not seem to be the entire answer because survival to adulthood for Thompson trout was also nil. We recommend that stocking of rainbow trout in Lake Superior tributaries be terminated until the causes of the low return are determined and corrected.